Heat shields of the generic type designated above are part of axial-throughflow turbine engines, through which gaseous working media flow for compression or controlled expansion and, because of their high process temperatures, those plant components which are acted upon directly by the hot working media are subject to high thermal loads. Particularly in the turbine stages of gas turbine plants, the rotating blades and guide vanes, arranged axially one behind the other in rotating blade and guide vane rows, are acted upon directly by the hot combustion gases occurring in the combustion chamber. In order to prevent the situation where the hot gases flowing through the flow channel subject to thermal load those regions within the turbine engine which are provided in stator regions facing away from the flow channel, heat shields, as they are known, which are provided on the stator side in each case between two guide vane rows arranged axially adjacently to one another, ensure as gastight a bridge-like sealing as possible between two guide vane rows arranged axially adjacently. Correspondingly designed heat shields may also be provided along the rotor unit, which are in each case mounted on the rotor side between two axially adjacent rotating blade rows, in order to protect corotating rotor components from the introduction of an excessive amount of heat.
Although the following statements refer solely to heat shields which are arranged between two guide vane rows and to that extent can separate and correspondingly protect the stator-side housing and the components connected to it with respect to the heat-loaded flow channel, it is also conceivable to provide the following measures on a heat shield which serves for protecting corotating rotor components and which can be introduced between two rotating blade rows arranged axially adjacently to one another.
FIG. 2a illustrates a diagrammatic longitudinal section through a gas turbine stage, into the flow channel of which project radially from outside guide vanes 1 connected to a stator housing S, the special configuration of which has no further significance in what follows.
A rotating blade 2, connected to a rotor unit, not illustrated, projects between two guide vanes 1 arranged adjacently in guide vane rows and is spaced apart radially on the end face with respect to a heat shield 3 which with the guide vane 2 encloses as small a free intermediate gap 4 as possible, in order as far as possible to avoid leakage losses of flow fractions of the hot gas stream through the intermediate gap 4. For this purpose, the rotating blade tip has sealing structures 5 which are arranged so as to rotate freely with respect to what are known as abrasion elements 6.
In order to avoid the situation where hot combustion gases in the region of the heat shield 3, which in a bridge-like manner spans the interspace between two guide vanes 1, 1′ arranged axially adjacently to one another, may penetrate into that region of the heat shield 3 which faces radially away from the flow channel, the heat shield 3 provides two axially opposite joining contours 7, 8 which extend axially into corresponding reception contours 9, 10 within the guide vane roots.
The reception contour 9 corresponds to a groove-shaped recess which is designed to be complementary with an exact fit to the joining contour 7 and which is incorporated in the root region of the guide vane 1. The axially opposite joining contour 8 of the heat shield 3 is likewise inserted into a reception contour 10 which is designed to be correspondingly complementary to the outer contour of the joining contour 8 and which is introduced in the root region of the guide vane 1′. However, the reception contour 10 has an axial clearance 11, so that the joining contour 8 is mounted axially slideably in the event of a corresponding operationally induced thermal expansion of the heat shield 3.
For the fluidtight sealing of the heat shield 3 with respect to the respective reception contours 9, 10 in the root regions of the guide vanes 1, 1′, seals 12, 13 are provided between the joining contours 7, 8 and the associated reception contours 9, 10. The seals 12, 13 are located each in a groove-shaped recess 14 within the joining contours 7, 8 (see also the illustration of a detail according to FIG. 2b of the joining region between the joining contour 8 and the reception contour 10). The seals 12, 13 are preferably manufactured from an elastic sealing material in the form of a round bar, project partially beyond the radially outer boundary surface 16 and fit flush, at least along a joining line, against the surface region 17 of the reception contour 10.
As a result of the sealing action of the seals 12, 13, it is possible, on the one hand, to avoid the situation where hot gases from the flow channel penetrate into the regions facing radially away from the flow channel, to the heat shield 3, and the situation is likewise prevented where cooling air L fed in on the stator side may pass through corresponding leakage points into the flow channel. As already explained initially, the clearance 11 provided in the recess 10 serves for a thermally induced material expansion along the heat shield 3, with the result that the joining contour 8, together with the seal 12 provided in it, is displaced into a position on the right, evident in the illustration. When, by contrast, the gas turbine stage is shut down and the individual components cool down, the joining contour 8, together with the seal 12 provided in it, returns to the original initial position. It is obvious that, due to the thermally induced relative movements between the reception contour 8 and the surface region 17, the seal 12 is subject to material abrasion phenomena which, when a maximum permissible tolerance limit is exceeded, lead to a wear- induced reduction in the sealing function of the seal, so that cooling air L can escape through the intermediate gaps which occur or are already present between the joining contour 8 and reception contour 10. This not only leads to a considerable loss of cooling air, with the result that the cooling action is drastically reduced, but there is also the risk that hot gases may also enter regions which face away from the flow channel with respect to the heat shield 3. In addition, usually seals are used which consist of a fabric material which may be thinned out under excessive mechanical frictional stress, with the result that the sealing action of the seal decreases with increasing operating time.